Just in case: another forum-member tried a Tokina 12-24 F/4 that weekend and one thing is for sure: The quality control of Tokina seems just as sh*tty as Sigmas.
So watch out where you buy! You should go to a dealer where you can easily swap or even give the lens right back, without a prohibitive restocking fee -----------
P.S.: Sometimes the 10mm of the Sigma can't be beat